1. Field of the Invention
The present invention relates to an internally plasticized copolymer of vinyl chloride, an alkyl acrylate and a bis (hydrocarbyl)vinylphosphonate.
2. Description of the Prior Art
External plasticizers in vinyl chloride homo- and copolymers are commonly employed today to form products having the required degree of flexibility for a given purpose. Such external plasticization, however, it not entirely satisfactory since the plasticizer tends to migrate to the surface and eventually is lost either by volatilization or extraction. This loss gives rise to such problems as surface stickiness, automotive windshield fogging and embrittlement of vinyl films containing the polymer which are used in such applications as shower curtains, baby pants, vinyl seat covers, and the like. Hence, various proposals for "internal plasticization" of vinyl chloride polymers have been made wherein the plasticizing action is supplied by one or more comonomers for vinyl chloride which are polymerized with the vinyl chloride to form the polymer.
The use of copolymers of a vinyl monomer and a polymerizable polyester, for example, an acrylate or a vinyl ester of a polyester of an aliphatic hydroxycarboxylic acid, was proposed in U.S. Pat. No. 3,640,927 to C. S. Marvel et al. An internally plasticized, two component vinyl chloride copolymer containing from about 75% to about 95% vinyl chloride and about 25% to about 5% of an ester of an unsaturated mono- or polycarboxylic acid, e.g., a C.sub.6 -C.sub.12 alkyl maleate, fumarate or acrylate, was proposed in U.S. Pat. No. 3,544,661 to A. Oth et al. A four component polymer composition vinyl chloride, a dialkyl maleate or fumarate, an alkyl ester of acrylic or methacrylic acid and a monohydrogen, monoalkyl maleate or fumarate was proposed in U.S. Pat. No. 3,196,133 to R. A. Piloni et al. for use as a solvent-based coating having both good adhesiveness and flexibility. In copending U.S. Ser. No. 795,990 filed May 11, 1977, by R. E. Gallagher et al. an internally plasticized copolymer of vinyl chloride, a C.sub.1 -C.sub.10 alkyl acrylate and a C.sub.8 -C.sub.22 dialkyl maleate or fumarate is disclosed.
Two component copolymers of vinyl chloride and such acrylates as 2-ethylhexyl acrylate, as seemingly suggested by certain portions of the Oth et al. patent produce heterogeneous resin compositions which do not show the desirable performance properties of flexible vinyl films of the present invention.
A variety of two component vinyl chloride/vinylphosphonate copolymers are known which cannot be classified as internally plasticized copolymers (U.S. Pat. Nos. 3,691,127, 3,792,113 and 3,819,770) since copolymerizing just vinyl chloride and a bis(hydrocarbyl)vinylphosphonate, e.g., bis(beta chloroethyl) vinylphosphonate, leads to production of a resin which gives a hard, relatively unflexible film requiring external plasticization. It does not appear to have been hitherto appreciated that a vinyl chloride/acrylate/vinylphosphonate copolymer, as described and claimed herein, would have flexibility characteristics as well as performance properties equivalent in many respects to externally platicized polyvinyl chloride without having to add a substantial amount of external plasticizer. Unexpectedly, the bis(hydrocarbyl)vinylphosphonate monomer aids in rendering the terpolymer less heterogeneous in appearance and resulting properties than if only vinyl chloride and an alkyl acrylate were used as comomers as suggested by certain prior art patents. The copolymers also has reduced smoke generation characteristics.